He was an easily scoring striker (24 goals in 55 national team matches). Sonck was able to jump high and had a strong header, despite his size. He was first selected on 2 June 2001 by Robert Waseige. He scored an important goal against Russia at the 2002 World Cup. He became an essential player for Aimé Anthuenis, in a team that was unable to qualify for a big tournament. Sonck became national U18 manager and was promoted in 2020 to lead the U19 team.